Hi TT. You need satellite-grade coaxial cable with f-connectors on either end. You can normally buy this sort of cable ready made up at a store such as Maplin, with luck at just the right length you need. Best to actually replace the existing cable entirely if you can; otherwise, you can add your new length of coax onto the existing one but you will need an extra little widget to make the two f-connectors marry up. Alsoe available at Maplins and very cheap.
Yes, it's technically against the T & Cs, but consider this - when they installed my broadband the tech left me a load of extra cable in case I ever fancied moving the modem somewhere else in the room. So they can't be that worried ...
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